Electrical control circuitry

ABSTRACT

Burner control apparatus includes lockout apparatus for deenergizing the control apparatus comprising a switch and an actuator for operating the switch after a time delay, first and second alternate lockout actuator energizing paths, a control device for actuating the ignition control means, and a timing circuit for providing an ignition timing interval of precise duration. The timing circuit is actuated in response to a request for burner operation and one of the lockout actuator energizing paths is completed in response to the actuated timing circuit. The control device is maintained energized if a signal from the flame sensor is received before the end of the ignition timing interval, and the control device is de-energized and a lockout actuator energizing path is completed in the absence of a signal from the flame sensor.

United States l atent 1191'.

Cade Oct. '8, 1974 ELECTRICAL CONTROL CIRCUITRY Primary Examiner-Edward G. Favors [75] Inventor: Philip J. Cade, Winchester, Mass. [73] Assignee: Electronics Corporation of America, [57] ABSTRACT Cambridge, Mass. Burner control apparatus includes lockout apparatus i for de-energizing the control apparatus comprising a [22] Filed 1974 switch and an actuator for operating the switch after a [21] Appl. No.: 432,525 time delay, first and second alternate lockout actuator energizing paths, a control device for actuating the ignition control means, and a timing circuit for providg" 431/ 12 4 553 ing an ignition timing interval of precise duration. The [58] Fie'ld 80 71 timing circuit is actuated in response to a request for a 431 3 7 burner operation and one of the lockout actuator energizing paths is completed in response to the actuated timing circuit. The control device is maintained ener- [56] References Cned gized if a signal from the flame sensor is received be- UNITED STATES PATENTS fore the end of the ignition timing interval, and the 3,376,099 4/1968 Giuffrida et al. 431/26 control device is de-energized and a lockout actuator 2,222,212 :33; fi l 33/ 5? energizing path is completed in the absence of a signal or 3,705,783 12/1972 Warren 431/78 from the name sensor 27 Claims, 3 Drawing Figures IO 24 T 14 PATENTEDom 8 am SHEET 3 0F 3 C316 9252mm mid ELECTRICAL CONTROL CIRCUITRY BACKGROUND OF THE INVENTION This invention relates to electrical control circuitry adapted for use in burner control systems.

Safety in burner operation is of the greatest importance in the design of burner control systems. Explosive concentrations of air and fuel may accumulate in the combustion chamber if fuel enters the chamber in the absence of a flame, a situation which might occur if ig nition does not take place within a reasonable time period after the ignition sequence is begun. To prevent a dangerous accumulation, the burner control locks out the system if ignition does not take place within a predetermined time interval after the ignition system is turned on--the trial-for-ignition time interval.

Typically, the timing function is performed by a lockout switch which is activated by being heated until it reaches a preset temperature. The heating process requires time to reach the temperature necessary for activation and thus provides a built-in time constant before the lock-out switch deactivates the system. Furthermore, a delay time is often provided before the ignition is turned on in order to permit purging of any fuel mixture present in the combustion chamber. This preignition delay time is often also provided by a thermal timer.

A problem encountered was that the thermal mass of ordinary thermally-actuated switches is too large to permit the short. trial-for-ignition time intervals desirable, and often necessary, in some applications. Adequate reproducibility of the time delay in such switches is impossible to obtain without exorbitant expense. A need therefore, exists in burner control technology for circuitry providing accurate, reproducible and short time delays at a reasonable price.

' A further problem encountered is to provide reliable and inexpensive circuitry for shutting down the burner system in the event of a loss of flame in the burner during normal operation while permitting ignition turn-on to be blocked if a flame signal is present when ignition is to be initiated after a call for burner operation.

SUMMARY OF THE INVENTION In accordance with the above, it is an object of this invention to provide a new and improved burner control apparatus featuring an accurate and reproducible trial-for-ignition time interval which may be shorter in duration than that normally obtainable by the use of thermally actuated switches.

It is a further object of this invention to provide a new and improved burner control apparatus with simple and reliable circuitry for responding to indications of malfunction such as an indication of loss of flame in the burner occurring after normal operation has been established and an indication of flame present when ignition is to be turned on.

ln accordance with a feature of the invention, there is provided burner control apparatus for use with a fuel burner installation having an operating control to produce a request for burner operation, a flame sensor to produce a signal when flame is present in the fuel burner installation and equipment responsive to the burner control apparatus for controlling fuel flow and ignition. The burner control apparatus includes a first actuator for actuating fuel ignition equipment, a sec- 0nd actuator for actuating fuel flow equipment, a normally open switch connected in series between the two actuators, fuel ignition control energizing circuitry responsive to a requestfor burner operation in the absence of a flame indicating signal from the flame sensor for energizing the first actuator, switch closing circuitry responsive to energizing of the first actuator for closing the normally open switch, fuel flow control energizing circuitry responsive to a flame indicating signal from the flame sensor when the switch is closed for energizing the second actuator and inhibiting circuitry responsive to a flame indicating signal from the flame sensor for preventing energization of the first actuator. The burner control apparatus also includes a' lock-out switch and associated circuitry for irreversibly turning the system off in case an indication of a malfunction appears.

In accordance with another feature of the invention there is provided burner control apparatus that includes lockout apparatus comprising a lockout switch and an actuator for operating the-lockout switch after a time delay, first and second alternate lockout actuator energizing paths, a control device for actuating an ignition control means, and a timing circuit for providing an ignition timing interval of precise duration. The apparatus further includes means responsive to a request for burner operation to initiate an ignition sequence by actuating the timing circuit, circuitry responsive to the actuated timing circuit for energizing the control device and completing one of thelockout actuator energizing paths, means responsive to a signal from a flame sensor to maintain the control device energized, and means responsive to the end of the ignition timing interval to de-energize the control device and to complete a lockout actuator energizing path in the absence of a signal from the flame sensor. 1

A further feature of the invention is time delay circuitry which de-energizes the first actuator in the absence of a flame indication from the flame sensor after a time delay produced by an electrical energy storage device.

In particular embodiments the ignition turn-on time interval begins after a time delay which permits purging of the burner installation and has a duration determined by the charging time of a capacitor in an RC network. The values of capacitors and resistors in the network may be chosen to provide short time intervals and accuracy and reproducibility are easily obtained. The ignition on-time is thus independent of other time constants in the circuit such as the length of time needed for the system to go to irreversible lock-out and the onset of the ignition on-time need not coincide with any of the other time period onsets, although it may do so.

Furthermore, in particular embodiments the normally open switch in series between the two actuators may be a transistor switch. This switch permits energization of the two actuators via a simple series circuit during normal operation thus facilitating shut-down of the main fuel flow in the event of loss of flame in the burner during normal operation. It also permits prevention of the onset of the ignition trial period if an indication of flame in the burner occurs prior to the ignition trial period using only a simple resistive network. The use of a transistor switch avoids the usual problems of contact corrosion, arcing and sticking which occur with the use of mechanical switch contacts.

Other objects, features and advantages of the invention will be seen as the following description of particular embodiments of the invention progresses, in conjunction with the drawings in which:

FIG. 1 is a schematic diagram of a combustion control system constructed in accordance with the invention;

FIG. 2is a schematic diagram of another form of combustion control system constructed in accordance with the invention; and

FIG. 3 is a schematic diagram of still another form of combustion control system constructed in accordance with the invention.

DESCRIPTION OF PARTICULAR EMBODIMENTS With reference to FIG. 1, the burner control arrangement includes terminals 10, 12 adapted to be connected to a suitable source of power. Connected directly across terminals 10, 12 is primary winding 14 of transformer 16 which has secondary windings 18 and 20 to provide power for the flame sensing circuitry 22. Also connected across terminals 10, 12 is a control section which includes a call-for-burner-operation switch 24, e.g., a thermostat, an alarm device 26, a blower motor 28, a pilot fuel control 30, an ignition device 32 and a main fuel control 34. A switch 36, controlled by air flow produced by blower 28, and the primary winding 38 of a second transformer 40 are connected in series between call-for-burner-operation switch 24 and power terminal 12 through a normally closed switch 42-2. The secondary winding 44 of transformer 40 has a full wave rectifier'circuit 46 connected across its terminals 48, 50 to provide d-c power for the control circuit at terminals 52, 54. Terminal 52 is connected to positive bus 56 and terminal 54 to ground bus 58.

The flame sensing circuitry 22 is connected across the secondary windings l8 and 20 of transformer 16. Connected to the high voltage terminal 60 of winding 20 is capacitor 62 in parallel with resistor 64. The parallel combination is connected in series with ultraviolet flame sensor 66 which in turn is connected to the low voltage terminal 68 of winding 18 through capacitor 70 in parallel with resistor 72. The output from the flame sensor circuitry 22 appears between grounded terminal 74 of winding 18 and terminal 76 of winding 20, which is connected to one terminal 78 of an inductor 80 which has two terminals 78, 82 and two taps 84, 86. Terminal 82 and tap 86 are connected via diodes 88 and 90 respectively through resistor 92 to the base of transistor 94 which amplifies the output of the flame sensor circuitry 22, fed to it through coupling network 96, and applies the amplified output to the base of transistor 98. The collector of transistor 94 is connected to positive bus 56 through resistor 100 and its emitter is connected to ground through resistor 102. The base of transistor 94 is also connected to ground through the parallel combination of resistor 104 and capacitor 106.

The control circuitry is connected between terminals 52, 54 of full-wave rectifier 46 and, includes a control relay actuator 108 which controls normally open contacts 108-1 and a flame relay actuator 110 which controls normally closed contacts 110-1 and normally open contacts 110-2.

The two relay actuators 108 and 110 are connected in series by transistor switch 112 as follows: one end of relay actuator is connected to the emitter of transistor 112 and one end of relay. actuator 108 to its collector. The other end of relay actuator 108 is connected to ground and the other end of relay actuator 110 is connected to positive bus 56 through transistor switch 98, which has its collector connected to relay actuator 110 and its emitter to positive bus 56. Connected to the junction between the collector of transistor 98 and relay actuator 110 is the parallel combination of resistor 114 and diode 116 which is connected to ground at its other end, providing a collector circuit for transistor 98 alternative to that containing the relay actuators 108 and 110. The non-grounded end of relay actuator 108 is connected through resistor 118 to the base of transistor 120, whose emitter is connected to ground, and to the emitter of transistor 122 and the emitter of Darlington pair 124. In series with transistor is the biasing resistor 126 for transistor 112, the other end of which is connected to positive bus 56. Transistor switch 112, which is between control relay actuator 108 and flame relay actuator 110, has its base connected to the collectorof transistor 120 through resistor 128, and is controlled by transistor 120. Premature-flame-signal resistor 130 has one end connected to the emitter of transistor 112 and the other end to the emitter of transistor 132 and prevents ignition if a flame signal is present before the ignition has been turned on.

The biasing resistors 134, 136 for transistor 122 are connected in series between the positive bus 56 and ground with the base of transistor 122 being connected to the junction of resistors 134 and 136. The collector of transistor 122 is connected to the base of transistor 138 through resistor 140, providing for control of transistor 138 by transistor 122 and the collector of transistor 138 is connected to ground. The emitter of transistor 138 is connected through resistor 142 to the junction of the collector of Darlington pair 124. and lockout switch actuator 42, which controls normally open contacts 42-1 and normally closed contacts 42-2, and which has its other end connected to positive bus 56. The series combination of transistor 138, resistor 142 and lock-out switch actuator 42 provides a first path for heating of lock-out switch actuator 42. The series combination of control relay actuator108, Darlington pair 124 and lock-out switch actuator 42 provides a second heating path.

Timing network 144 provides a delay before ignition is begun and consists of the series combination of capacitor 146 and resistor 148 (connected respectively to the positive bus 56 and the ground bus 58) and associated circuitry. Connected to the junction of capacitor 146 and resistor 148, is the emitter of transistor 132. The collector of transistor 132 is connected to the base of transistor 150 and through resistor 152, to the positive bus 56. The base of transistor 132 is connected to the positive bus 56 through biasing resistor 154 and to ground through biasing resistors 156 and 158. The collector of transistor 150 is connected to the junction of resistors 156 and 158 and its emitter topositive bus 56.

A second timing network 160 provides for a limited ignition trial time and consists of the series combination of capacitor 162 attached to the collector of transistor 150 and resistors 164 and 166, with resistor 164 attached to ground. The base of Darlington pair 124 is connected to the junction between resistors 164 166.

In operation, the main power switch is turned on applying power to input terminals 10, 12. Transformer 16 has its primary winding 14 energized which energizes secondary windings 18 and 20 of transformer 16 applying power to the flame sensor 66 through resistorcapacitor combinations 72, 70 and 64, 62 respectively.

and

In response to a request for burner operation, a signaled by the closing of call-f0r-burner-operation switch 24, power is applied to blower motor 28 through normally closed contacts 42-2. When air flow from blower motor 28 is sensed, normally open air flow switch contacts 36 are closed applying power to the primary winding 38 of transformer 40 and energizing the secondary winding 44 of transformer 40. A positive d-c voltage appears at terminal 52 of full-wave rectifier 46 and terminal 54 is grounded. Immediately after power is applied to the circuit, capacitor 146 is uncharged and the emitter of transistor 132 is at the positive bus voltage. Transistor 150 is biased off which places the base of the Darlington pair 124 close to ground potential and thus biases it off. ln the absence of a flame signal from flame sensor circuitry 22, transistor 98 is non-conducting. Transistor 120 is non-conducting since its base is tied to ground through resistor 118 and relay actuator 108. Transistor 112 is also non-conducting, since it is controlled by transistor 120 and is designed to be nonconducting when transistor 120 is non-conducting.

Two processes are initiated when power is applied to transformer 40. The biasing network comprised of resistors 134 and 136 turns on transistor 122 which in turn provides base current through resistor 140 for transistor 138 which conducts in turn and which initiates heating of lock-out switch actuator 42 through the first heating path. At the same time, pre-ignition delay timing capacitor 146 begins to charge. As capacitor 146 charges with a time constant determined by the product of its capacitance with the resistance of resistor- 148, the voltage difference across capacitor 146 rises, causingthe emitter of transistor 132 to approach ground potential and thus causing transistor 132 to conduct. When transistor 132 conducts, current flows through resistor 152, the voltage on the base of transistor 150 drops and transistor 150 turns on. Transistor l50.when conducting shunts resistors 154 and 156, increasing the current through resistor 158, and thus raising the potential on the base of transistor 132 causing it to conduct more strongly and latching it in the conducting state. Also when transistor 150 conducts, its collector potential rises close to the positive bus voltage, initiating charging of trial-for-ignition timing capacitor 162. Capacitor 162 does not begin significant charging until transistor 150 conducts. Prior to that time, the potential on capacitor 162 is low due to the proportioning of resistors 154, 156 and 158 in the voltage divider network. The increased collector potential of transistor 150, when it conducts, also provides a bias potential for Darlington pair 124 through the bias network of transistor 150, capacitor 162 which is substantially uncharged, resistor 164 and resistor 166, and the Darlington pair 124 conducts through a path including lock-out switch actuator 42 and control relay actuator 108. The current flowing through this path has three effects. lt continues the heating of lock-out actuator 42. It shunts transistors 122 and 138, turning them off and opening the first heating path. It also energizes relay actuator 108 causing normally open switch contacts 108-l to close which both permits flow of the pilot fuel 30 and turns on ignition 32 via normally closed contacts 110-1. Thus after a suitable delay determined by timing network 144, the ignition and pilot fuel are turned on and heating of the lock-out switch actuator, begun when power was first applied to the circuit, is continued. The current through relay actuator 108 also raises the base potential of transistor 120 through resistor 118 causing transistor 120 to conduct and to turn on transistor 112, thus connecting relay actuators 108 and 110 in series.

As capacitor 162 charges, the potential at the base of Darlington pair 124 drops towards ground potential. After a time determined essentially by the capacitance of capacitor 162 and the series resistance of resistors 164 and 166, Darlington pair 124 is turned off. In normal operation a flame signal from flame sensor circuitry 22 appears during the charging time of capacitor 162 at the base of transistor 94, and is amplified by transistor 94. The resulting signal is applied to the base of transistor 98, turning it on and completing a maintaining path through relay. actuators 108 and 110 and conducting transistor 112. The resulting current flowing through flame relay actuator 110 turns off the ignition by opening normally closed contacts 110-1 and initiates main-fuel flow by closing normally open contacts 110-2. Lock-out actuator 42 heating stops because both heating paths are i opened, the first by nonconducting transistor 138 and the second by nonconducting Darlington pair 124.

If no flame signal from the flame sensing circuitry 22 is received, transistor 98 would remain nonconducting, limiting current flow through flame relay actuator 110 and causing contacts 110-1 to remain closed and contacts 110-2 to remain open. The small current flowing in the path including resistor 152, conducting transistor 132, prematur e-flame-signal resistor 130, relay actuator 110 and resistor 114, is insufficient to actuate the relay contacts. When Darlington pair 124 ceases to conduct, the potential difference across relay actuator 108 drops to a value close to zero. The control relay contacts 108-l drop out atthis point turning off both fuel and ignition. Transistor 120 turns off,

turning off transistor 112. Flame relay actuator 110 has never been energized and remains in that state. Transistor 122 turns on again and turns on transistor 138. Current flows through transistor 138, resistor 142 and lock-out switch actuator 42, continuing to heat the lock-out switch actuator which after a time delay,

opens normally closed contacts 42-2, thus shutting off the entire system and closes normally open contacts 421 which activates alarm 26.

If, after the establishment of normal operation, the flame signal from flame sensing circuitry 22 were to be lost, indicating a loss of flame in the burner apparatus, transistor 98 would cease to conduct, breaking the maintaining path through relay actuators 108 and and turning off the fuel by opening contacts 110-2 and preventing ignition or pilot fuel flow by opening contacts 108-1. No current flows in control relay actuator'l08, and the emitter of transistor 122 is therefore at ground potential. Transistor 122 conducts, turning on transistor 138 as in normal operation and a current flow path including transistor 138, resistor 142 and lock-out switch actuator 42 is completed, causing heating of lock-out switch actuator 42. The ignition sequence cannot be reinitiated because capacitor 162 is fully charged and thus Darlington pair 124 cannot conduct. The system then proceeds to lock-out status.

If a flame signal from flame sensing circuitry 22 is present when a call for burner operation is received, indicating either the presence of flame in the burner or malfunction of the flame sensing circuitry 22, transistor 98 would be turned on through the alternate collector circuit including resistor 114 and diode 116. Relay actuator 110 is not energized since transistor switch 112, which is not conducting, breaks the series circuit of the two relay actuators 110 and 108. The voltage on the collector of transistor 98 is close to the positive bus voltage and the voltage on the emitter of transistor 112 is also close to that voltage since little current flows in relay actuator 110. Premature-flame-signal resistor 130 clamps the emitter of transistor 132 close to the positive bus voltage and capacitor 146 cannot charge sufficiently to cause transistor 132 to conduct. Thus the ignition sequence cannot begin and the system goes to lock-out status in response to the current in the first heating path.

A second embodiment is shown in FIG. 2. Components that are the same or similar to those in the embodiment shown in FIG. 1 are identified with the same reference numeral. Control circuitry is connected between terminals 52, 54 of full wave rectifier 46 and includes a control relay actuator 108 and flame relay actuator 110. The two relay actuators are connected in series with flame'responsive transistor 98, diode 200, transistor switch 202, and resistors 204 and 206 between positive bus 56 and negative bus 58.

Lockout switch actuator 42 has two heating paths, a first path through transistor 212 and a second path through'Darlington pair 214 in series with resistor 206 and control relay actuator 108. The circuit also includes atiming capacitor 220 that is connected in series with resistor 222, diode 224 and resistors 226, 228 and 230 to negative bus 58. Connected to the junction between'diode 224 and resistor 226 is blocking diode 232 that is connected to the base of transistor 234 which has its collector in turn connected to the base of transistor 236 and to resistor 230. The emitter of transistor 236 is connected to the junction between the base of transistor 212 and resistor 230 and the collector of transistor 236 is connected to resistor 222. Resistor 238 and resistor 240 form a voltage divider network connected to the emitter of transistor 234; a capacitor 242 is connected between the emitter and base of transistor 234; and feedback resistor 244 is connected between the collector of transistor 236 and the base of transistor 234. The junction between resistors 226 and 228 is connected to the junction between transistor 98 and flame relay coil actuator 110.

Connected across capacitor 220 is diode 246 and connected to the junction between timing capacitor 220 and diode 224 is diode 248 and resistors 250, 252 in series with lockout heater 42. Diode 254 and resistor 256 form a network connected to the base of transistor 258 which in turn controls Darlington pair 214.

In operation, in response to a call for burner operation, blower 28 is energized and when air flow switch 36 closes, power is applied via transformer 40 and rectifier 46 to terminals 52 and 54, energizing the control circuitry. As capacitor 220 charges, the voltage at the junction between diodes 224 and 232 drops towards the voltage on the negative bus 58, controlling a first (preignition) timedelay interval as a function of the RC values of the capacitor charging circuit. When capacitor 220 is sufficiently charged to turn on transistor 234, the resulting current flow turns on transistor 236. That action latches transistor 234 in conduction and connects the plus side of capacitor 220 to resistor 230, abruptly dropping the voltage applied to diode 248. This voltage transition is coupled by resistor 250 and turns off transistor 258 and turns on the Darlington pair 214. Current flow through the lockout actuator 42, the Darlington pair 214, resistor 206 and control relay actuator 108 pulls in that relay. The current flow through this path thus initiates heating of the lockout actuator 42; and energizes relay actuator 108 causing normally open switch contacts 108-l to close, initiating an ignition condition by permitting flow of pilot fuel through control 30 and turning on the ignition transformer through control 32. The current through relay actuator 108 also raises the base potential on transistor 262 causing that transistor to conduct and clamp the base of transistor 212 to the negative bus 58, preventing turn on of transistor 212. Conduction of transistor 262 also turns on transistor 260 which in turn turns on series switch transistor 202. r

As capacitor 220 discharges, the potential at the base of transistor 258 rises. After a time interval determined essentially by the capacitance of capacitor 220 and the resistances of actuator 42 and resistors 252 and 250, transistor 258 is again turned on, turning off Darlington pair 214. In normal operation, during this discharging interval of capacitor 220 and prior to turn off of Darlington pair 214, a flame signal from flame sensor circuitry 22 appears at the base of transistor 94 and is applied to the base of transistor 98, turning that transistor on and completing a relay actuator maintaining path through actuators 108 and and conducting transistor switch 202. The pickup of actuator 110 turns off the ignition by opening normally closed contacts 110-1 and initiates the main fuel flow by closing normally opened contacts 110-2. Heating of the lockout 42 stops because both of its heating paths are open, the first by non-conducting transistor 212 and the second by nonconducting Darlington pair 214.

If a flame signal is not received from the flame sensing circuitry, transistor 98 would remain nonconducting. When Darlington pair 214 ceases to conduct, the potential difference across relay actuator 108 drops and the control relay drops out, opening contacts 108-1 turning off fuel and ignition controls. Transistor 262 turns off and transistor 212 turns on, completing a second heating path for lockout actuator 42. The lockout actuator thus continues to heat and at the end of its time delay opens normally closed contacts 42-2, shutting down the burner system and closes normally opened contacts 42-2, energizing alarm 26.

If, after establishment of normal burner operation, the flame signal disappears, indicating loss of flame in the burner apparatus, transistor 98 ceases to conduct, breaking the maintaining path through relay actuators 108 and 110 and with the drop out of those relays contacts 108-1 and 110-2 open, turning off fuel flow. As no current is flowing in control relay actuator 108, transistor 262 turns off, causing transistor 212 to conduct and establish a current flow path for lockout actuator 42 through transistor 212. An ignition sequence is not reinitiated and the system proceeds to lockout status.

If a flame signal from flame sensing circuitry 22 is present when a call for burner operation is received,

indicating either the presence of flame or malfunction in the flame sensing circuitry, transistor 98 would be turned on. Relay actuator 110 is not energized since transistor switch 202 is not conducting, and as the voltage on the collector of transistor 98 is close to the voltage on positive bus 56, capacitor 220 cannot charge sufficiently to switch transistor 236 into conduction, thus preventing start of the ignition sequence. Transistor 212 is turned on and current flow through actuator 42 causes the system to go to lockout status.

A third embodiment is shown in FIG. 3. Only those parts of the circuit are shown which are significantly different from the other embodiments. Terminals 300 and 302 are connected to a source of DC power which is energized in response to a call for burner operation. Switch 304 represents a means for delaying onset of the ignition sequence after a call for burner operation and is in series between terminal 300 and positive bus 306.

Lock-out switch actuator 308 is connected to positive bus 306 and controls normally open contacts and normally closed contacts, used to actuate the alarm system and shut downoperation of the burner respectively. Connected to the other end of the lock-ut switch actuator 308 are a pair of parallel actuating paths. The first includes transistors 310 and 312 and the second includes transistor 314 and silicon controlled rectifier (SCR) 316. in the first path the collector of transistor 310 is connected to lock-out switch actuator 308, its emitter to the collector of transistor 312 and the emitter of transistor 312 is connected to the junction of resistor 318 and diode 320 thus providing a path to ground through diode 320. In the second path, lock-out switch actuator 308 is connected to the emitter of transistor 314, the collector of transistor 314 to the anode ofSCR 316 and the cathodeof SCR 316. to the junction of resistor 318 and diode 320 and thence to ground through diode 320. Connected to the emitter of transistor 310 is resistor 322 in series with resistor 324 to ground, providing a gate signal source to SCR 316 from the junction of resistors 322 and 324.

Also connected to positive bus 306, and forming the timing network for the trial-for-ignitiontime, is resistor 326 in series with timing capacitor 328, resistor 330 and flame relay actuator 332 to ground. Flame sensing circuitry 346 is connected across actuator 332. The base of transistor 234 is connected to the junction of capacitor 328 and resistor 330, its emitter is connected to ground through diode 320 and its collector is connected to the base of transistor 336 through resistor 338. The emitter of transistor 336 is connected to positive bus 306 and its collector to ground via control relay actuator 340 in series with resistors 342 and 344. The base of transistor 310 is connected for biasing to the junction of resistors 342 and 344. The junction of resistor 330 and flame relay actuator 332 is connected to the junction of isolator resistor 348 that is connected directly to the base of transistor 312 and isolator resistor 350 that is attached directly to the base of transistor 314.

In operation, in response to a call for burner operation, DC power is applied to terminals 300, 302. After 10 a time delay for warmup and/or purging, pre-ignition time delay switch 304 is closed, energizing the control circuitry.

In normal operation, no flame signal from the flame sensing circuitry 346 is present at this time. The bases of transistors 312 and 314 are close to ground potential. The emitter of transistor 314 is close to the B+ potential on positive bus 306 and thus transistor 314 is conducting. The emitter of transistor 312 on the other hand is close to ground potential and transistor 312 remains non-conducting. Since capacitor 328 is uncharged at this time, the bias on the base of transistor 334 is determined by resistors 326 and 330 and transistor 334 conducts, providing base current for transistor 336 through resistor 338 and causing transistor 336 to conduct as well. Most of the emitter-collector current through transistor 336 goes through control relay actuator 340 and resistors 342 and 344, generating enough voltage on the base of transistor 210 to turn it on and current flows through resistors 322 and 324 in its emitter circuit. This current flow generates a positive gating voltage at the gate of SCR 316, turning it on. The current through relay actuator 340 and the low impedance path including SCR 316 and transistor 336 is large enough to activate the actuator 340' and to turn on both ignition and pilot fuel. A conduction path for lock-out switch actuator heating is established through diode 320, SCR 316, transistor 314 and the lock-out switch actuator 308. SCR 316 forms a shunt across the biasing network for transistor 310 which reduces the voltage on the base of transistor 310 close to ground potential and causes that transistor to turn off. Also when switch 304 is closed, capacitor 328 begins to charge and together with resistors 326 and 330 forms a timing network to determine the period of ignition. The current through relay actuator 322 due to charging of the capacitor 328 is not large enough to activate the relay.

At some time during the period of ignition, a flame signal from flame sensing circuitry 346 should appear across relay actuator 332 in normal operation.'The flame signal will consist of a positive voltage close to the B+ voltage. The flame signal will accomplish three objectives. First, capacitor 328 will stop charging and will in fact discharge since the potential difference across capacitor 328 will be small. Transistor 336 will remain on. Second, transistor 314 will turn off, since its emitter-base voltage will be lowered by the imposition of the flame signal at its base through resistor 350. The conduction path for heating lock-out switch actuator 308 which includes SCR 316 and transistor 314 is opened by the turn-off of transistor 314. The second conduction path for heating lock-out switch actuator 308 through transistor3l0 and 312 is also opened, because transistor 310 is not conducting. Lastly, the flame signal causes current flow through' flame relay actuator 332, which turns on the main fuel and turns off the ignition. This is the maintaining configuration for the system.

if no flame signal is received from flame sensing circuitry 346, indicating that the pilot fuel has failed to ignite, no significant current flows through relay actuator 332 and the main fuel is not turned on. Transistor 312 will remain non-conducting. Transistor 314 remains on, which continues heating of lock-out switch actuator 308. Timing capacitor 328 continues to charge and the current through resistors 326 and 330 as well as through relay actuator 332 continues to drop. The potential on the base of transistor 334 drops towards ground potential and transistor 334 turns off, turning off transistor 336. The current through relay actuator 340 drops to a value too small to maintain the relay in its energized state and thus both ignition and pilot fuel are turned off. The system proceeds to lock-out status via the conduction path for heating of the lock-out switch actuator 308 including diode 320, SCR 316 and transistor 314.

If after the establishment of normal operation the flame signal is lost, the current through flame relay actuator 332 cannot maintain the flame relay in its energized state and the main fuel flow is turned off. Transistor 314 conducts, beginning heating of the lock-out switch actuator via diode 320, SCR 316 and transistor 314. As capacitor 328 charges, the voltage on the base of transistor 334 drops and, if flame is not reestablished, after a time determined by the time constant of the network including capacitor 328 and resistances 326 and 330, transistor 334 turns off which turns off transistor 336, causing relay actuator 340 to deenergize and turn off the ignition and" pilot fuel flow. The system proceeds to lock-out status via the conduction path including diode 320, SCR 316, and transistor 314.

If a flame signal is present when a request for burner operation is received, transistor 314 is turned off through resistor 350 and transistor 312 is turned on. Transistors 334, 336 and 310 are turned on in the normal sequence. However, transistor 312, which is on,

shunts the bias network consisting of resistors 322 and 324 and no gate signal is generated to cause SCR 316 to fire. The high-current path for actuation of relay actuator 340 including transistor 33,6, relay actuator 340 and SCR 316 thus is blocked and the alternate lowcurrent flow to actuate the control relay. Thus the ignition and pilot fuel controls arenever turned on and the system goes to lock-out status via the conduction path including diode 320, transistors 312 and 310 and lockout switch actuator 308.

While particular embodiments of the invention have been shown and described, various modifications will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiments or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

l. Burner control apparatus for use with a fuel burner installation having an operating control to produce a request for'burner operation, a flame sensor to produce a signal when flame is present in said fuel burner installation, and means responsive to said burner control apparatus for controlling fuel flow and fuel ignition, said burner control apparatus comprising lockout apparatus for de-energizing said control apparatus comprising a switch and an actuator for operating said switch after a time delay,

first and second alternate lockout actuator energizing paths,

a control device for actuating said ignition control means,

a timing circuit for providing an ignition timing interval of precise duration,

means responsive to a request for burner operation to initiate an ignition sequence by actuating said timing circuit,

circuitry responsive to said actuated timing circuit for energizing said control device and completing one of said lockout actuator energizing paths,

means responsive to a signal from said flame sensor to maintain said control device energized, and

means responsive to the end of said ignition timing interval to de-energize said control device and to complete a lockout actuator energizing path in the absence of a signal from said flame sensor.

2. The apparatus as claimed in claim 1 wherein said first lockout actuator energizing path includes a solid state switching device responsive to said timing circuit for completing said first path during said ignition timing interval.

3. The apparatus as claimed in claim 1 wherein said timing circuit includes an RC timing network to produce said ignition timing interval.

4. The apparatus as claimed in claim 1 and further including a second timing circuit for providing a preignition timing interval of precise duration and wherein said request responsive means actuates said second timing circuit and said ignition timing interval is initiated in response to the end of said pre-ignition timing interval.

5. The apparatus as claimed in claim 4 wherein each said timing circuit includes an RC timing network to produce its respective timing interval.

6. The apparatus as claimed in claim 5 wherein said first and second timing circuits utilize a common capacitor, the timing interval of one of said timing circuits being a function of the charging of said common capacitor and the timing interval of the other timing circuit being a function of the discharging of said common capacitor.

7. The apparatus as claimed in claim 1 wherein said first lockout actuator energizing path includes a first solid state switching device responsive to said timing circuit for, completing said first path throughout said ignition timing interval independent of a signal from said flame sensor.

8. The apparatus as claimed in claim 7 wherein said second lockout actuator energizing path includes a second solid state switching device responsive to said first solid state switching device for completing said second path in the absence of a signal from said flame sensor after the end of said ignition timing interval.

9. The apparatus as claimed in claim 8 and further including means responsive to said request for burner operation for causing said second solid state switch to complete said second path prior to said ignition timing interval.

10. The apparatus as claimed in claim 1 and further including a second control device responsive to a signal from said flame ,sensor for actuating a fuel control means, a normally open switch, and circuitry responsive to energization of said first control device for closing said switch to connect said first and second control devices in series.

11. The apparatus as claimed in claim 1 and further including inhibiting means responsive to said flame sensor signal prior to energization of said first control device for preventing energization of said first control device.

12. The apparatus as claimed in claim 11 wherein said inhibiting means includes a circuit connected between said second control device and said first timing 13 I circuit for preventing initiation of said ignition timing interval.

13. The apparatus as claimed in claim 11 and further including a second control device responsive to a signal from said flame sensor for actuating a fuel control means, a normally open switch, and circuitry responsive to energization of said first control device for closing said switch to connect said first and second control devices in series.

14. The apparatus as claimed in claim 13 and further including a second timing circuit for providing a preignition timing interval of precise duration and wherein said request responsive means actuates said second timing circuit and said ignition timing interval is initiated in response to the end of said pre-ignition timing interval.

15. The apparatus as claimed in claim 14 wherein each said timing circuit includes an RC timing network to produce its respective timing interval.

16. The apparatus as claimed in claim 15 wherein said first lockout actuator energizing path includes a first solid state switching device responsive to said timing circuit for completing said first path throughout said ignition timing interval independent of a signal from said flame sensor.

17. The apparatus as claimed in claim 16 wherein said second lockout actuator energizing path includes a second solid state switching device responsive to said first solid state switching device for completing said second path in the absence of a signal from said flame sensor after the end of said ignition timing interval.

18. The apparatus as claimed in claim 17 and further including means responsive to said request for burner operation for causing said second solid state switch to complete said second path prior to said ignition timing interval.

19. The apparatus as claimed in claim 18 wherein said inhibiting means includes a circuit connected between said second control device and said first timing circuit for preventing initiation of said ignition timing interval. 1

20. The apparatus as claimed in claim 15 wherein said first and second timing circuits utilize a common capacitor, the timing interval of one of said timing circuits being a function of the charging of said common capacitor and the timing interval of the other timing circuit being a function of the discharging of said common capacitor.

21.. The apparatus as claimed in claim 20 wherein said inhibiting means includes a circuit connected to said common capacitor for preventing charging of said one capacitor when said flame sensor signal is present.

22. Burner control apparatus for use with a fuel burner installation having an operating control to produce a request for burner operation, a flame sensor to produce a signal when flame is present in said fuel burner installation and means responsive to said burner control apparatus for and means responsive to said burner control apparatus for controlling fuel flow and fuel ignition, said burner control apparatus comprising a first actuator for actuating said fuel ignition control means,

a second actuator for actuating said fuel flow control means,

a normally open switch connected in series between said first actuator and said second actuator,

fuel ignition control energizing circuitry responsive to a request for burner operation in the absence of a flame signal from said flame sensor for energizing said first actuator,

switch closing circuitry responsive to energizing of said first actuator for closing said normally open switch,

fuel flow control energizing circuitry responsive to said signal from the flame sensor when said switch is closed for energizing said second actuator, and

inhibiting circuitry responsive to said signal from the flame sensor when said switch is open for preventing energization of said first actuator.

23. Burner control apparatus for use with a fuel burner installation having an operating control to produce a request for burner operation, a flame sensor to produce a signal when flame is present in said fuel burner installation and means responsive to said burner control apparatus for controlling fuel flow and fuel ignition, said burner control apparatus comprising a first actuator for actuating said fuel ignition control means, r

a second actuator for actuating said fuel means,

fuel ignition control energizing circuitry responsive to a request for burner operation in the absence of a flame signal from said flame sensor for energizing said first actuator,

fuel flow control energizing circuitry responsive to said signal from said flame sensor for energizing said second actuator,

inhibiting circuitry responsive to said signal from said flame sensor prior to energization of said first actuflow control ator for preventing energizing of said first actuator,

and

time delay circuitry including an electrical energy storage device for producing a time delay, said time delay circuitry being operative in the absence of said signal from said flame sensor to de-energize said first actuator at the end of said time delay.

24. Burner control apparatus as claimed in claim 23,

said burner control apparatus further including a lock-out switch to shut down burner operation,

a lock-out switch actuator to activate said lock-out switch after said lock-out switch actuator has been energized for a preset time period, and

circuitry for energizing said lock-out switch actuator, said circuitry to become inoperative if fuel ignition is accomplished before said lock-out switch actuator has been energized for said preset time period.

tion of said first actuator. 

1. Burner control apparatus for use with a fuel burner installation having an operating control to produce a request for burner operation, a flame sensor to produce a signal when flame is present in said fuel burner installation, and means responsive to said burner control apparatus for controlling fuel flow and fuel ignition, said burner control apparatus comprising lockout apparatus for de-energizing said control apparatus comprising a switch and an actuator for operating said switch after a time delay, first and second alternate lockout actuator energizing paths, a control device for actuating said ignition control means, a timing circuit for providing an ignition timing interval of precise duration, means responsive to a request for burner operation to initiate an ignition sequence by actuating said timing circuit, circuitry responsive to said actuated timing circuit for energizing said control device and completing one of said lockout actuator energizing paths, means responsive to a signal from said flame sensor to maintain said control device energized, and means responsive to the end of said ignition timing interval to de-energize said control device and to complete a lockout actuator energizing path in the absence of a signal from said flame sensor.
 2. The apparatus as claimed in claim 1 wherein said first lockout actuator energizing path includes a solid state switching device responsive To said timing circuit for completing said first path during said ignition timing interval.
 3. The apparatus as claimed in claim 1 wherein said timing circuit includes an RC timing network to produce said ignition timing interval.
 4. The apparatus as claimed in claim 1 and further including a second timing circuit for providing a pre-ignition timing interval of precise duration and wherein said request responsive means actuates said second timing circuit and said ignition timing interval is initiated in response to the end of said pre-ignition timing interval.
 5. The apparatus as claimed in claim 4 wherein each said timing circuit includes an RC timing network to produce its respective timing interval.
 6. The apparatus as claimed in claim 5 wherein said first and second timing circuits utilize a common capacitor, the timing interval of one of said timing circuits being a function of the charging of said common capacitor and the timing interval of the other timing circuit being a function of the discharging of said common capacitor.
 7. The apparatus as claimed in claim 1 wherein said first lockout actuator energizing path includes a first solid state switching device responsive to said timing circuit for completing said first path throughout said ignition timing interval independent of a signal from said flame sensor.
 8. The apparatus as claimed in claim 7 wherein said second lockout actuator energizing path includes a second solid state switching device responsive to said first solid state switching device for completing said second path in the absence of a signal from said flame sensor after the end of said ignition timing interval.
 9. The apparatus as claimed in claim 8 and further including means responsive to said request for burner operation for causing said second solid state switch to complete said second path prior to said ignition timing interval.
 10. The apparatus as claimed in claim 1 and further including a second control device responsive to a signal from said flame sensor for actuating a fuel control means, a normally open switch, and circuitry responsive to energization of said first control device for closing said switch to connect said first and second control devices in series.
 11. The apparatus as claimed in claim 1 and further including inhibiting means responsive to said flame sensor signal prior to energization of said first control device for preventing energization of said first control device.
 12. The apparatus as claimed in claim 11 wherein said inhibiting means includes a circuit connected between said second control device and said first timing circuit for preventing initiation of said ignition timing interval.
 13. The apparatus as claimed in claim 11 and further including a second control device responsive to a signal from said flame sensor for actuating a fuel control means, a normally open switch, and circuitry responsive to energization of said first control device for closing said switch to connect said first and second control devices in series.
 14. The apparatus as claimed in claim 13 and further including a second timing circuit for providing a pre-ignition timing interval of precise duration and wherein said request responsive means actuates said second timing circuit and said ignition timing interval is initiated in response to the end of said pre-ignition timing interval.
 15. The apparatus as claimed in claim 14 wherein each said timing circuit includes an RC timing network to produce its respective timing interval.
 16. The apparatus as claimed in claim 15 wherein said first lockout actuator energizing path includes a first solid state switching device responsive to said timing circuit for completing said first path throughout said ignition timing interval independent of a signal from said flame sensor.
 17. The apparatus as claimed in claim 16 wherein said second lockout actuator energizing path includes a second solid state switching device responsive to said first solid state switchinG device for completing said second path in the absence of a signal from said flame sensor after the end of said ignition timing interval.
 18. The apparatus as claimed in claim 17 and further including means responsive to said request for burner operation for causing said second solid state switch to complete said second path prior to said ignition timing interval.
 19. The apparatus as claimed in claim 18 wherein said inhibiting means includes a circuit connected between said second control device and said first timing circuit for preventing initiation of said ignition timing interval.
 20. The apparatus as claimed in claim 15 wherein said first and second timing circuits utilize a common capacitor, the timing interval of one of said timing circuits being a function of the charging of said common capacitor and the timing interval of the other timing circuit being a function of the discharging of said common capacitor.
 21. The apparatus as claimed in claim 20 wherein said inhibiting means includes a circuit connected to said common capacitor for preventing charging of said one capacitor when said flame sensor signal is present.
 22. Burner control apparatus for use with a fuel burner installation having an operating control to produce a request for burner operation, a flame sensor to produce a signal when flame is present in said fuel burner installation and means responsive to said burner control apparatus for and means responsive to said burner control apparatus for controlling fuel flow and fuel ignition, said burner control apparatus comprising a first actuator for actuating said fuel ignition control means, a second actuator for actuating said fuel flow control means, a normally open switch connected in series between said first actuator and said second actuator, fuel ignition control energizing circuitry responsive to a request for burner operation in the absence of a flame signal from said flame sensor for energizing said first actuator, switch closing circuitry responsive to energizing of said first actuator for closing said normally open switch, fuel flow control energizing circuitry responsive to said signal from the flame sensor when said switch is closed for energizing said second actuator, and inhibiting circuitry responsive to said signal from the flame sensor when said switch is open for preventing energization of said first actuator.
 23. Burner control apparatus for use with a fuel burner installation having an operating control to produce a request for burner operation, a flame sensor to produce a signal when flame is present in said fuel burner installation and means responsive to said burner control apparatus for controlling fuel flow and fuel ignition, said burner control apparatus comprising a first actuator for actuating said fuel ignition control means, a second actuator for actuating said fuel flow control means, fuel ignition control energizing circuitry responsive to a request for burner operation in the absence of a flame signal from said flame sensor for energizing said first actuator, fuel flow control energizing circuitry responsive to said signal from said flame sensor for energizing said second actuator, inhibiting circuitry responsive to said signal from said flame sensor prior to energization of said first actuator for preventing energizing of said first actuator, and time delay circuitry including an electrical energy storage device for producing a time delay, said time delay circuitry being operative in the absence of said signal from said flame sensor to de-energize said first actuator at the end of said time delay.
 24. Burner control apparatus as claimed in claim 23, said burner control apparatus further including a lock-out switch to shut down burner operation, a lock-out switch actuator to activate said lock-out switch after said lock-out switch actuator has been energized for a preset time period, and circuitry for energizing said lock-ouT switch actuator, said circuitry to become inoperative if fuel ignition is accomplished before said lock-out switch actuator has been energized for said preset time period.
 25. Burner control apparatus as claimed in claim 24, said time delay circuitry including an RC timing network to produce said time delay.
 26. Burner control apparatus as claimed in claim 25 further including an RC timing network for providing a time delay before said fuel ignition control energizing circuitry energizes said first actuator.
 27. Burner control apparatus as claimed in claim 26 further including a normally open switch connected in series between said first actuator and said second actuator, said switch being closed in response to energization of said first actuator. 